Wednesday, October 17, 2018

Look beyond the can to maximise wild oat control

April 30, 2018 by  
Filed under Crops

Growers are being advised to adopt an integrated approach to wild oat control this spring – by embracing chemical and cultural control methods in tandem.

Modern weed control protocols should look beyond the herbicide for maximum efficacy and employ a twin-track approach to reduce the bank of unwanted seeds, says David Roberts, herbicide technical specialist for Adama.

“Wild oats are one of the most competitive weeds affecting modern arable rotations with just one plant per square metre able to reduce winter cereal yields by as much as 1.0t/ha, and spring yields by as much as 0.6 t/ha,” says Mr Roberts.

“Growers need to use all available tools to control weeds this spring, but in doing so shouldn’t rely solely on chemical herbicides.  After all, an over-reliance on any single mode of action could see their efficacy fall away, as has been seen with fungicide resistance in recent years.”

Emergence window

Controlling wild oats is complicated by their protracted emergence window, says Mr Roberts, who says growers should integrate herbicides with non-chemical control methods. “While they can germinate in the autumn, the majority of seedlings will appear in the spring.

“This wide germination window, plus the ability of large wild oat seeds to propagate from depths of up to 15cm, means some cultural control methods such as delayed drilling, spring cropping and ploughing can be less effective against wild oats than they are against blackgrass.

That said, growers shouldn’t be discouraged from using cultural control methods. “If anything, I’d positively encourage growers to implement changes to their cropping strategy, rotation, and cultivation practices in order to safeguard the longevity and efficacy of current herbicides.”

But Mr Roberts warns that cultural practices such as spring cropping may encourage spring-germinating common wild oats. This means any changes to existing farming practices must be carefully planned in order to avoid replacing one pressure with another, he says.

Spring germination

Direct drilling is advisable, for example, when trying to combat the threat of spring germination. This is because the reduction in soil disturbance can limit the number of seeds that germinate – leading to fewer problems.

As with any weed control protocol, the first point of focus should be to prevent unwanted seed ingress. “This essentially means preventing the importation and spread of seeds by ensuring all rented or contractor machinery is fully decontaminated prior to use.”

Beyond that, growers should carry out hand-roguing or spray off distinct patches of weeds before they start shedding seeds in areas where weed populations are relatively restricted. Weed mapping should be used to identify and monitor where infestations have occurred.

“Having a definitive understanding of where weeds are growing and how they are spreading or regressing is the only truly accurate way of determining if current control protocols are having the desired effect.

Cropping cycle

“Being able to substantiate or refute existing measures will help to develop a more effective herbicide, cultivation and cropping strategy for the next cropping cycle.”

Where weed infestations are more widespread – and beyond the control of roguing or selective spraying, Mr Roberts recommends the use of an appropriate post-emergence herbicide.

ACCase inhibitor herbicides such as Topik (240 g/l clodinafop-propargyl and 60 g/l cloqunitocet-mexyl) are effective at controlling wild oats in wheat, while pinoxaden can be used in crops of barley, he says.

“Pre-emergence herbicides more commonly used for the control of other grassweeds can also provide some control of wild oats, but their success will depend on the target weed’s emergence pattern.

“The inclusion of a non-cereal break crop such as oilseed rape also enables the use of alternative herbicides, including propaquizafop, quizalofop, cycloxydim, clethodim, carbetamide and propyzamide, further reducing reliance on any single mode of action.”

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